1. Field of the Invention
This invention relates to vanadium spinel materials in the V.sub.2 O.sub.3 --MnO--SiO.sub.2 system.
2. Summary of the Invention
The present invention pertains to vanadium spinel materials and a method for their preparation. The material comprises vanadium spinels containing vanadium in the trivalent state. The drawing shows a polygon in a ternary composition diagram of V.sub.2 O.sub.3, MnO and SiO.sub.2. The material falling within said polygon represents compositions of liquids within the ternary system V.sub.2 O.sub.3 --MnO--SiO.sub.2 with which said spinel phase is in equilibrium on the liquidus surface and from which the spinel phase is crystallized. The polygon shaped shaded area has the vertices and corresponding coordinates in weight percent as shown in Table I.
TABLE I ______________________________________ Coordinates (wt %) Vertices V.sub.2 O.sub.3 MnO SiO.sub.2 ______________________________________ A 44 55 1 B 25 55 20 C 25 35 40 D 59 1 40 E 98 1 1 ______________________________________
A method of preparing a vanadium spinel material that is crystallized from a liquid with which said vanadium spinel is in equilibrium on the liquidus surface, and wherein said liquid has a composition that falls within a polygon shaped area ABCDE as shown in the disclosed FIGURE for a ternary composition diagram of V.sub.2 O.sub.3, MnO and SiO.sub.2 comprises the steps of:
(1) heating V.sub.2 O.sub.5 powder having a particle size of less than about 50 microns in an atmosphere in which the partial pressure
of oxygen is in the range of 10.sup.-5 to 10.sup.-10 atmosphere and the CO.sub.2 /H.sub.2 volume ratio is in the range of about 10/1 to 1/1 while gradually increasing the temperature stepwise over a temperature range of about 600.degree. C. to 1300.degree. C. and holding the final temperature for a period of at least about 24 hrs. to ensure complete reduction of all vanadium to V.sup.3+ ;
(2) heating MnO powder having a particle size of less than about 50 microns for a period of about 10 to 14 hrs. at a temperature in the range of about 1200.degree. C. to 1400.degree. C.;
(3) heating SiO.sub.2 powder having a particle size of less than about 50 microns for a period of about 10 to 14 hours at a temperature in the range of about 1000.degree. C. to 1200.degree. C.;
(4) thoroughly grinding together an amount of V.sub.2 O.sub.3 from (1) in the range of about 25 to about 98 wt.%, with an amount of MnO from (2) in the range of more than 0 to about 55 wt.%, and with an amount of SiO.sub.2 from (3) in the range of about more than 0 to about 40 wt.% to produce a mixture having a grain size of less than about 50 microns,
(5) pelletizing the mixture from (4) at a pressure of about 5,000 psi;
(6) heating the pellets from (5) at a temperature in the range of about 1200.degree. C. to 1600.degree. C. for a period in the range of about 12 to 48 hrs. in an atmosphere in which the partial pressure of oxygen is in the range of 10.sup.-10 to 10.sup.-5 atmosphere to produce a melt; and
(7) cooling the material from (6) and crystallizing out said vanadium spinel material, and separating said vanadium spinel material from the rest of the melt.